[Intel-gfx] [PATCH v3 4/6] drm/i915/guc: don't spinwait if the GuC's workqueue is full

[Dave Gordon]

Rather than wait to see whether more space becomes available in the GuC
submission workqueue, we can just return -EAGAIN and let the caller try
again in a little while. This gets rid of an uninterruptable sleep in
the polling code :)

We'll also add a counter to the GuC client statistics, to see how often
we find the WQ full.

v3:
    Flag the likely() code path (Tvtrko Ursulin).

Signed-off-by: Dave Gordon <david.s.gordon at intel.com>
---
 drivers/gpu/drm/i915/i915_debugfs.c        |  1 +
 drivers/gpu/drm/i915/i915_guc_submission.c | 18 +++++++-----------
 drivers/gpu/drm/i915/intel_guc.h           |  8 ++++----
 3 files changed, 12 insertions(+), 15 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
index 6ad008c..9e215e6 100644
--- a/drivers/gpu/drm/i915/i915_debugfs.c
+++ b/drivers/gpu/drm/i915/i915_debugfs.c
@@ -2506,6 +2506,7 @@ static void i915_guc_client_info(struct seq_file *m,
 	seq_printf(m, "\tWQ size %d, offset: 0x%x, tail %d\n",
 		client->wq_size, client->wq_offset, client->wq_tail);
 
+	seq_printf(m, "\tWork queue full: %u\n", client->no_wq_space);
 	seq_printf(m, "\tFailed to queue: %u\n", client->q_fail);
 	seq_printf(m, "\tFailed doorbell: %u\n", client->b_fail);
 	seq_printf(m, "\tLast submission result: %d\n", client->retcode);
diff --git a/drivers/gpu/drm/i915/i915_guc_submission.c b/drivers/gpu/drm/i915/i915_guc_submission.c
index 9e30762..21d3603 100644
--- a/drivers/gpu/drm/i915/i915_guc_submission.c
+++ b/drivers/gpu/drm/i915/i915_guc_submission.c
@@ -469,26 +469,22 @@ static void guc_fini_ctx_desc(struct intel_guc *guc,
  */
 int i915_guc_wq_check_space(struct drm_i915_gem_request *request)
 {
-	const size_t size = sizeof(struct guc_wq_item);
+	const size_t wqi_size = sizeof(struct guc_wq_item);
 	struct i915_guc_client *gc = request->i915->guc.execbuf_client;
 	struct guc_process_desc *desc;
-	int ret = -ETIMEDOUT, timeout_counter = 200;
+	u32 freespace;
 
 	GEM_BUG_ON(gc == NULL);
 
 	desc = gc->client_base + gc->proc_desc_offset;
 
-	while (timeout_counter-- > 0) {
-		if (CIRC_SPACE(gc->wq_tail, desc->head, gc->wq_size) >= size) {
-			ret = 0;
-			break;
-		}
+	freespace = CIRC_SPACE(gc->wq_tail, desc->head, gc->wq_size);
+	if (likely(freespace >= wqi_size))
+		return 0;
 
-		if (timeout_counter)
-			usleep_range(1000, 2000);
-	};
+	gc->no_wq_space += 1;
 
-	return ret;
+	return -EAGAIN;
 }
 
 static int guc_add_workqueue_item(struct i915_guc_client *gc,
diff --git a/drivers/gpu/drm/i915/intel_guc.h b/drivers/gpu/drm/i915/intel_guc.h
index b37c731..436f2d6 100644
--- a/drivers/gpu/drm/i915/intel_guc.h
+++ b/drivers/gpu/drm/i915/intel_guc.h
@@ -73,10 +73,10 @@ struct i915_guc_client {
 
 	/* GuC submission statistics & status */
 	uint64_t submissions[GUC_MAX_ENGINES_NUM];
-	uint32_t q_fail;
-	uint32_t b_fail;
-	int retcode;
-	int spare;			/* pad to 32 DWords		*/
+	uint32_t no_wq_space;		/* Space pre-check failed	*/
+	uint32_t q_fail;		/* Failed to queue (MBZ)	*/
+	uint32_t b_fail;		/* Doorbell failure (MBZ)	*/
+	int retcode;			/* Result of last guc_submit()	*/
 };
 
 enum intel_guc_fw_status {
-- 
1.9.1